Electrical-motor-driven devices are widely utilized. However, it is difficult to monitor the operating condition of such motors and devices without removing the motor from service. When such motor-driven-devices are in service, it is possible to measure voltage imbalance, high harmonic content of currents and voltages, motor and ambient temperatures, etc., which affect motor efficiency.
In fact, the ability to detect degradations of electrical-motor-driven systems without removing the motor from service is especially important where motors are used in safety and/or cost sensitive situations, for example, in nuclear generating stations and computer chip manufacturing plants. Additionally, the ability to calculate on-line motor torque output and motor efficiency, with a confirmation that the calculations are correct, is very important in many situations where electrical-motor-driven devices are utilized. These abilities can be very useful in reducing energy consumption and motor replacement costs in installations where large numbers of motors are used.
Attempts have been made to provide methods and apparatuses for monitoring the condition of electrical motors. For example, U.S. Pat. No. 4,442,393 to Abbondanti describes an apparatus and method for monitoring the operation of an induction motor. Based upon the sensed input voltages and the currents fed into a standard induction motor, the motor overall reactance, the motor overall real impedance, the air gap resistance, the parallel combination of stator and rotor leakage reactances, and the stator leakage reactance are derived. These operating characteristics are then utilized to control torque produced by the motor.
Additionally, U.S. Pat. No. 4,888,996 to Rak et al. describes a method and apparatus which utilizes motor armature current, voltage drop across the armature, and the electrical resistance of the armature for generating mechanical values of motor output mechanical power, armature speed, and a motor torque factor representative of the motor torque multiplied by a constant. The method and apparatus described by Rak et al. were developed to address the problems associated with the assessment of D.C. motors.
Nothing in the prior art, however, discloses a remote on-line process monitoring and diagnostic system such as that embodied by the subject invention. Specifically, nothing in the prior art discloses the subject method or apparatus for the remote assessment of a motor's rotor speed, power output, efficiency and torque.